We plan to pursue our discovery that air oxidized cholesterol be mutagenic towards strains of Salmonella typhimurium. Air-oxidized sterols of other structures and sterols oxidized under other conditions will be tested. Mutagenic batches of cholesterol will be fractionated by chromatography into defined subfractions which will then be tested for mutagenicity, thereby to define which oxidized sterols may be responsible for the observed mutagenicity. Individual sterol components will ultimately be isolated and identified as active mutagens. Defined sterols will also be tested as pure sterols in order to exclude known components of the air-oxidized cholesterol preparations as mutagens.